Breast cancer is the most common cancer except for skin cancer among women in the United States. Each year, more than 200,000 American women are diagnosed to have breast cancer. Depending on the type, stage of the cancer and other factors, patients with breast cancer may be treated by surgery, radiation, and other forms of therapy. Surgery involves removal of breast lumps (lumpectomy) or all of the breast tissue (mastectomy). Radiation therapy uses high-energy radiation such as X-rays or gamma rays to destroy cancer cells. Radiation therapy may be used either alone or in conjunction with surgery, chemotherapy or other forms of therapy. Most patients receive radiation therapy after lumpectomy to destroy cancer cells that may remain in the area after lumpectomy. Some patients receive radiation therapy before surgery to shrink the tumor to a manageable size to enable surgical excision.
Various types of radiation therapy are known. Brachytherapy, or internal radiation therapy, involves invasive placement of radioactive substances directly into the breast tissue adjacent to the tumor. Surgical procedures are required to place e.g. catheters into the breast to help guide radioactive materials into the correct area of the breast.
Conventional external beam radiation therapy employs a radiation source outside the body to deliver high energy radiation to the tumor. The radiation source typically includes a relatively large accelerator and electronics, making it difficult to be positioned close to the body for highly localized therapy such as accelerated partial breast irradiation. In addition, because external radiation beam must pass through the skin to reach the tumor, the skin is necessarily subjected to, and often higher, radiation dose than the tumor. Depending on the severity of the skin toxicity of radiation, the resultant damages include erythema (reddening of the skin), which may cause patient discomfort, and desquamation (ulceration and denudation of the skin), which is painful and often requires that the therapy be interrupted.